Improvements in the processing capability of communications devices have been accompanied by a marked increase in signal speed. As signal speed increases, control of characteristic impedance is essential in order to assure a good high-frequency characteristic. With regard to transmission between printed wiring boards incorporated in communications devices, not only is use made of conventional backplane transmission but now there are also situations where use must be made of a coaxial cable through the intermediary of a coaxial connector. Further, even with conventional backplane transmission there are cases where measurement and evaluation are carried out in order to implement the backplane transmission, and in such cases a coaxial connector must be employed to connect the printed wiring board and the measurement equipment.
With regard to a case where a printed wiring board is equipped with a coaxial connector [e.g., a BNC (Bayonet Neil-Concelman) connector or SMA (Sub-Miniature Type-A) connector], the principal causes of a degraded characteristic, i.e., a characteristic impedance mismatch, are considered to be the following three: First, an impedance mismatch of the very through-hole formed in the printed wiring board for the purpose of accommodating the coaxial connector; second, an impedance mismatch at the portion connecting from the through-hole to signal wiring; and third, an impedance mismatch, which is ascribable to a stub (branch), that occurs in a signal through-hole. The following techniques have been proposed as means for eliminating such impedance mismatch:    [Patent Document 1] Japanese Patent Kokai Publication No. JP-P2003-217745A    [Patent Document 2] Japanese Patent Kokai Publication No. JP-P2004-165200A    [Patent Document 3] Japanese Patent Kokai Publication No. JP-P2004-327690A    [Patent Document 4] Japanese Patent Kokai Publication No. JP-P2005-175189A    [Patent Document 5] Japanese Patent Kokai Publication No. JP-P2005-351731A    [Patent Document 6] Japanese Patent Kokai Publication No. JP-8-274513A    [Patent Document 7] Japanese Patent Kokai Publication No. JP-P2005-5539A    [Patent Document 8] Japanese Patent Kokai Publication No. JP-P2003-86954A